import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

class Request{
    public String aa;
    public String bb;
}
class Response{
    public String aa;
    public String bb;
}
@WebServlet("/json")
public class json extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        Request request = objectMapper.readValue(req.getInputStream(),Request.class);

        Response response = new Response();
        response.aa = request.aa;
        response.bb = request.bb;
        String ans = objectMapper.writeValueAsString(response);
        resp.setContentType("application/json; charset=utf8");
        resp.getWriter().write(ans);
    }
}
